The modern warewasher or dishwasher, to a large extent, provides a time effective way to efficiently and thoroughly wash large volumes of dishes. A typical dishwasher directs sprays of wash solution and/or rinse water (hereinafter generically referred to as "wash fluid") at the surface of dirty dishes or other wares supported on racks or trays in order to remove any dirt and/or food particles from the dirty dishes. Commonly, the wash fluid may include a diluted active agent such as a detergent and/or a sanitizing agent.
Many dishwashers utilize one or more rotatable wash arm assemblies to direct a pressurized spray of wash fluid onto the dishes from multiple directions. The typical wash arm mechanism includes a rotatable wash arm that is internally supplied with a flow of wash fluid. The fluid enters the wash arm at a pressure sufficient to generate a spray out of small holes in the wash arm. The holes are spaced out along the length of the wash arm, and may be oriented in different directions, so as to maximize the area covered by the spray. Furthermore, the holes in the wash arm are oriented to provide a net torque sufficient to spin the wash arm and increase the effective area covered by the spray.
Wash arm mechanisms typically include structure for communicating wash fluid to the wash arm and structure for permitting the wash arm to rotate. Commonly, these two functions are provided by a single wash arm hub, so that wash fluid is supplied to the wash arm through the rotatable coupling for the wash arm.
The prior art discloses numerous mechanisms to support and to supply fluid to the wash arm. For example, U.S. Pat. No. 5,165,435 discloses such a support assembly where a low friction washer supports a wash arm hub. An annular flange is used to rotatably connect the wash arm hub to a fluid supply means, typically using a bolt or knob. The tightness of this bolt or knob typically increases the tightness of the seal between the wash arm hub and the annular flange. Increased tightness, however, also increases the rotatable friction between the wash arm hub and the annular flange. Another example of such an arrangement is U.S. Pat. No. 3,160,164.
These designs trade off the tightness of the seal provided by the wash arm hub and the resulting friction. In other words, the looser the fit between the wash arm assembly and the support structure, the greater the amount of fluid leakage and pressure loss. A tighter fit, however, increases rotational friction between the support structure and the wash arm. This trade off is critical because high fluid pressure and sufficient fluid supply are necessary to spin the rotatable wash arm and efficiently clean dishes. Stubbornly attached particles often require a long exposure to a hot, high pressure spray. Consequently, fluid which leaks from the wash arm hub increases the total amount of fluid required to clean the dishes. Furthermore, stubbornly attached particles may need to be impacted by a spray from numerous directions. Consequently, free rotation of the wash arm improves the overall cleaning qualities of the automatic dishwasher.
Some machines have attempted to overcome the fluid supply pressure limitation by using a powerful motorized pump. As a result, the seal/friction trade off becomes less important because the pump supplies an excess of pressure sufficient to overcome the high friction associated with typical fluid supply and support mechanisms. Such complicated mechanisms typically make the replacement of worn seals difficult. Furthermore, although the increased pressure decreases the importance of the seal/friction trade off, such a design increases the amount of fluids used.
Other standard wash arm designs have primarily sought to use two types of unsealed bearings: sleeve or roller. A sleeve bearing, such as sleeve bearing 100 shown in FIG. 1, simply provides a low friction sleeve 104 between a hub 102 and a wash arm 106. This design allows for easy replacement, however, it also results in significant leakage and comparatively large rotational friction which wears the hub components. Alternately, a roller bearing, such as roller bearing 110 shown in FIG. 2, may provide a low friction support for a wash arm. Roller bearing 110 uses inner and outer races of bearings 120, 122 which are enclosed by a hub nut 112 and hub spindle 116. Inner race 120 is also supported by a hub bushing 114. A ring retainer 118 prevents hub spindle 116 from moving relative to hub bushing 114. This configuration works to reduce lateral rotational friction resulting from the spinning of a wash arm and vertical rotational friction resulting from the support of a wash arm. Roller bearings 120, 122, typically constructed of stainless steel, typically wear well. The main disadvantage of this design, however, is that it allows fluid to flow past the bearing races 120, 122, and therefore may leak a significant amount of fluid.
Still other designs have simply accepted high fluid loss in favor of reduced friction. For example, U.S. Pat. No. 3,064,665 uses ball bearings to support a shaft connected to an upper reaction rotatable wash arm. This device, however, also typically allows significant leakage between the fluid supply means and the support shaft.
In view of the foregoing, a number of problems result from the limitations of the existing designs. For example, automatic dishwashers which use wash arms with conventional hubs end up consuming more wash fluid, including more water and more active agent (e.g., detergent or sanitizing agent). As a certain amount of spray volume is necessary to remove certain attached particles, the fluids leaked through a conventional hub must be supplied by additional total volume to maintain the same degree of washing efficiency.
Also, a conventional hub requires an increased amount of energy to be expended to heat the additional fluids. Both such requirements have obvious economic and environmental disadvantages.
Additionally, the cycle time required to adequately clean dirty dishes typically increases to supply the additional fluids leaked through a conventional hub. This decreases the overall volume of dishes that may be washed by the dishwasher in a given period of time.
Therefore, a need exists for a wash arm hub which provides low friction and therefore allows easy rotation, while having reduced leakage through the hub, thereby exhibiting decreased fluid and energy consumption, as well as decreased cycle time.